This invention relates to a wire fabric used in the reinforcement of concrete pipes.
Various forms of wire fabric have been proposed which upon fabrication into a cylindrical cage or elliptical cage shape are employed to reinforce concrete pipe. These fabrics generally include a plurality of transverse wire strands and a plurality of circumferential defining line strands. The fabric is typically provided to the pipe manufacturer by the fabric manufacturer in the form of a continuous roll or in sheets manufactured to size. The transverse strands have generally been spaced at 6, 8 or 12 inch intervals and when fabric is supplied in a continuous roll the pipe manufacturer has had to count the number of transverse wires to determine the correct length for a predetermined size of pipe. The fabric must then be cut, formed into a circular or elliptical cage and the ends of circumferential line strands of the fabric overlapped and secured together as by welding.
This procedure has resulted in a substantial amount of wasted fabric and increased fabrication time and cost due to the necessity of counting the transverse wires or spacings, required to yield a particular length of fabric for a predetermined cage for the pipe size. The spacing between the transverse wires or strands most generally yields a fabric length greater than the fabric length required for the circumference of the pipe reinforcing cage. Many of these problems have been alleviated by the wire fabric disclosed in U.S. Pat. No. 3,990,480, entitled METHOD AND FABRIC FOR MAKING REINFORCING CAGES, and filed on Jan. 20, 1975 by Wilbur E. Tolliver and Daniel J. Borodin. The disclosed fabric therein is divided into sets of transverse strands with each set separated by a space smaller than the spacing of transverse strands within each set. This results in a readily discernable severance or cut line for the shear operator and eliminates the necessity of counting transverse strands or spacing, to yield a length of fabric required for the predetermined pipe size. The fabric is made so that each set has a length corresponding to the circumference of the predetermined pipe size, for example. This fabric and method of making and using same substantially reduces the waste of the fabric from that heretofore experienced as well as increasing the efficiency of wire cage production.
Additional problems, however, are presented which are not solved by this fabric. For example, reinforcement requirements of certain classes of concrete pipe can best be furnished by including additional reinforcement or steel area at the quadrants of the cage wherein the maximum stresses in the concrete pipe occur. On the inside reinforcement cage the maximum stresses occur at the crown and the invert of the pipe and on the outside reinforcement cage at the spring lines of the pipe. Additional steel area is required in the quadrants which include the points of maximum stress. This additional reinforcement has generally been provided by cutting the predetermined fabric lengths, rolling or forming the fabric into a reinforcing cage, connecting the ends of the cut fabric and then tack welding properly dimensioned fabric mats or quadrant mats to the cage at the quadrants where additional steel reinforcement is required.
Also, it is sometimes advantageous or required to provide additional reinforcement in the form of stirrups at the point of maximum stress at the pipe crown and invert. The stirrups are projections, which when secured to the fabric in the areas of the maximum stress quadrants, extend radially outwardly from the cage. The stirrups have typically been attached to the fabricated pipe reinforcing cage resulting in the need for substantial more labor to complete the cage.